Refrigeration of one fluid by heat exchange with another



June 11, 1963 H. HASHEMl-TAFRESHI 3,092,976

REFRIGERATION OF ONE FLUID BY HEAT EXCHANGE WITH ANOTHER FiledJune 1. 1961 F/G/ 2&[ 25 23 2/ 19 /7 27 26 29 3 J? 24 22 20 l8 l6 "I 1: U 30 4 5 6 a /o /2 A an fi m'Aemz' 72 1/2146 Inventor United States Patent Ofiice 3,092,976 Patented June 11, 1963 3,092,976 REFRIGERATION OF ONE FLUID BY HEAT EXCHANGE WITH ANOTHER Hadi Hashemi-Tafreshi, London, England, assignor to Conch International Methane Limited, Nassau, The Bahamas, a Bahamian company Filed June 1, 1961, Ser. No. 114,198 6 Claims. (Cl. 62-117) This invention relates to a novel method of refrigeration.

The basic principle involved in refrigerating systems of the compression type is that of transferring heat from an environment at low temperature to one at a higher temperature by causing a volatile liquid, usually called the refrigerant, to absorb heat at the low temperature by vapourisation and to dissipate this heat at the high temperature by condensation. Vapourisation and condensation are respectively induced by maintaining a lower or higher pressure than the saturation pressures of the refrigerant at the lower and higher temperatures.

This system in which heat is absorbed by the refrigerant during its evaporation requires that the whole of the vapour produced be compressed from the lowest pressure in the system to the highest. If the evaporation took place in stages, each at a lower pressure, the total compressor work required to recompress these gases to the highest pressure in the system would be less. Up to the present, the only way of achieving this reduction in work has been to have a series of the evaporation heat exchangers operating at successively lower pressures but this involves a considerable amount of plant.

We have now found that if in a refrigeration system of the compression type the refrigerant is caused to absorb heat while being maintained in a'liquid condition, and the vapourisation takes place in stages thereafter, a considerable saving in compressor work is effected without having to use a plurality of evaporator heat exchangers.

Accordingly, the present invention provides a method of cooling a first fluid with a second fluid which comprises:

(a) passing the second fluid as a liquid at a temperature lower than that of the first fluid in indirect heat exchange with thefirst fluid, the pressure of the second fluid being such that it remains as a liquid throughout such heat exchange step;

(b) expanding the warmed second fluid from the heat exchange step in two or more expansion chambers in series to produce a cold second fluid as a liquid and, from each expansion chamber, a cold second fluid as a recompressing the liquid from step (b) and recycling it to step (a);

(d) recompressing and liquefying and gases from step (b), said liquefaction being effected by indirect heat exchange with a third fluid, and

(e) recycling the compressed liquid expansion chambers of step (b).

from step (d) to the Preferably in step (d) the gas from each expansion chamber is recompressed to the pressure of the gaseous efl'luent from the previous expansion chamber and is fed into such eflluent for further recompression with it.

It is also possible to insert one or more expansion chambers in the path of the compressed liquid from step (d) to join up with the series of expansion chambers used in step (1)).

Also if desired, subsidiary refrigeration can be obtained by using liquid from any of the expansion chambers in a normal evaporator type heat exchanger, recycling the vapour produced to an appropriate compressor used in step (d).

The liquefaction in step (d) may of course be achieved by indirect heat exchange with two or more cold fluids if so desired.

The second fluid used in the method of this invention, i.e. the refrigerant, may be any suitable volatile liquid or liquefiable gas, for example, ammonia, carbon dioxide, sulphur dioxide, dichloroethylene, dichlorodifluoromethane, methane, ethane, ethylene, propane, or butane.

The invention will now be illustrated by reference to the accompanying drawings in which FIGURE I is a flow sheet of an ethylene refrigeration cycle used to cool another fluid, for example natural gas at 1500 p.s.i.a., from 20 F. to 200 F., and FIGURE II is a flow sheet of an ammonia refrigeration cycle used to cool another fluid, for example ethylene at 300 p.s.i.a.,, from F. to F.

Referring to FIGURE I the fluid to be cooled from --20 F. to -200 F., for example natural gas at 1500 p.s.i.a., is passed through pipe 1 in heat exchanger 2. In this heat exchanger the cooling is achieved by liquid ethylene at 320 p.s.i.a. and an inlet temperature of 205" F. passing through pipe 3. The liquid ethylene leaves the heat exchanger at 32 F. but is still a liquid. This liquid passes to expansion valve 4 and then into expansion chamber 5, the drop in pressure being sufiicient to lower the temperature in expansion chamber 5 to 63 F. The liquid from expansion chamber 5 passes to expansion chamber 7 the pressure being reduced in expansion valve 6 'by an amount suflicient to reduce the temperature to -l02 F. The liquid from expansion chamber 7 passes to expansion chamber 9 through expansion valve 8, the drop in pressure being suflicient to reduce temperature in expansion chamber 9 to 13l F. The liquid in expansion chamber 9 passes to expansion chamber 11 via expansion valve 10, the drop in pressure being suflicient to reduce the temperature in expansion chamber 11 to 174 F. The liquid in expansion chamber 11 passes to expansion chamber 13 via expansion valve 12, the drop in pres sure being suflicient to reduce the temperature in expan sion chamber 13 to 206 F.

The liquid from expansion chamber 13 is passed via pipe 14 to compressor 15 in which its pressure is raised to 320 p.s.i.a. From compressor 15 the liquid passes via pipe 3 through heat exchanger 2 to complete the cycle.

The gas phase in expansion chamber 13 at 206 F. and 1.8 p.s.i.a. passes via pipe 16 to compressor 17 in which the gas is raised to 7.5 p.s.i.a. This gas is mixed with the gas leaving expansion chamber 11 in pipe 18 and passed to compressor 19 in which the gas is compressed to 30 p.s.i.a. The gas leaving compressor 19 joins with the gas from expansion chamber 9 in pipe 20 and is fed to compressor 21. The exit gases from compressor 21 at 65 p.s.i.a. are joined with the gas from the expansion chamber 7 in pipe 22 and fed to compressor 23. The exit gases from compressor 23 at p.s.i.a. are mixed with the gas from expansion chamber 5 in pipe 24 and are fed to compressor 25.

The exit gases from compressor 25 at 300 p.s.i.a. are then liquefied by passage, firstly through water cooler 26, secondly through heat exchanger 27, in which they are cooled from 100 F. to 20 F. by indirect heat exchange with liquid ammonia at 25 F. and 250 p.s.i.a. passing through pipe 28, and, thirdly, through heat exchanger 29 in which they are liquefied at 20 F. by indirect heat exchange with evaporating liquid ammonia in pipe 30.

The liqued ethylene at -20 F. then passes via pipe 31 and expansion valve 32 into expansion chamber 5 to complete the gas cycle.

As already explained, it is expansion chambers in the from step (d), of expansion possible to insert one or more path of the compressed liquid referred to above, to join up with the series chambers used in step (b). This can be achieved, for example, in a modification of the flow sheet of FIGURE I made by joining the pipe carrying the liquid ethylene after it leaves heat exchanger 2 to expansion valve 6 instead of expansion valve 4. Naturally with such a change the temperature and pressure conditions will have to be altered somewhat.

Referring to FIGURE II, the fluid to be cooled from 100 F. to F. passes through pipe in heat exchanger 41 in which it is cooled by indirect heat exchange with liquid ammonia passing through pipe 42 at an inlet temperature of -25 F. and a pressure of 250 p.s.i.a. The liquid ammonia leaving the heat exchanger 41 still as a liquid at 75 F., passes through expansion valve 43 into expansion chamber 44, the drop in pressure being suflicient to lower the temperature in expansion chamber 44 to 51 F. The liquid from expansion chamber 44 passes through expansion valve 45 to expansion chamber 46, the drop in pressure being sufiicient to lower the temperature to 9 F. The liquid from expansion chamber 46 passes to expansion chamber 47 via expansion valve 48, the drop in pressure being suflicient to reduce the temperature to 26 F. The liquid from expansion chamber 47 is divided into two streams, one of which passes through pipe 49 to compressor 50. The compressed liquid from compressor 50 at 250 p.s.i.a. passes through pipe 42 to complete the cycle.

The other portion of the liquid from expansion chamber 47 passed through pipe 51 and heat exchanger 52 in which it evaporates While further cooling or liquefying the fluid originally cooled in heat exchanger 41. For example, if the fluid in pipe 40 is ethylene and this leaves heat exchanger 41 at F. it can be liquefied at -20 F. in the evaporator heat exchanger 52.

After passing through heat exchanger 52 the ammonia in vapour form is mixed via pipe 53 with the gaseous effluent from expansion chamber 47 in pipe 54 and fed to compressor 55. The exit gas from compressor 55 at 37.6 p.s.i.a. joins the gas from expansion chamber 46 in pipe 56 and is fed to compressor 57. The compressed gas from compressor 57 at 91 p.s.i.a. is coiled in water cooler 58 and then joins the gas from expansion chamber 44 in pipe 59 and passes to compressor 60. The compressed ammonia from compressor 60 passes through water cooler 61 in which it is liquefied at 100 F., and thence through expansion valve 62 into expansion chamber 44 to complete the gas cycle. If it is desired to cool the compressor suction, a part of the liquid ammonia leaving water cooler 61 can be fed back via pipes 63, 64 and 65 to appropriate stages Preferably all the compressors in this ammonia refrigeration system are reciprocating compressors.

in the gas compression system. r

I claim.

1. A method of cooling a first fluid with a second fluid which comprises:

(a) passing the second fluid as a liquid at a temperature lower than that of the first fluid in indirect heat exchange with the first fluid, the pressure of the second fluid being such that it remains as a liquid throughout such heat exchange step;

(b) expanding the warmed second fluid from the heat exchange step in a plurality of expansion chambers in series to produce a cold second fluid as a liquid and, from each expansion chamber, a cold second fluid as a gas;

(0) recomprcssing the liquid from step (b) and recycling it to step (a);

(d) recompressing and liquefying the gases from step (b), said liquefaction being effected by indirect heat exchange with a third fluid, and

(e) recycling the compressed liquid from step (d) to the expansion chambers of step (b).

2. A method as claimed in claim 1 in which the gas from each expansion chamber is recompressed to the pressure of the gaseous effluent from the previous expansion chamber and is fed into such eflluent for further recompression with it.

3. A method as claimed in claim 2 which includes expansion of the liquid resulting from the recompression and liquefaction of the gases from the expansions in step (b) prior to expansions in the expansion chambers of step (b) in which a further expansion chamber is inserted in the path of the compressed liquid resulting from the recompressing and liquefying of the gases from the said expansion chambers to join up with the said series of expansion chambers.

4. A method as claimed in claim 2 in which subsidiary refrigeration is obtained by passing liquid from one of the expansion chambers to an evaporator type heat exchanger and recycling the vapour produced to the appropriate compressor used in recompressing the gases from an expansion chamber.

5. A method as claimed in claim 2 in which the second fluid is selected from the group of refrigerants consisting of ammonia, carbon dioxide, sulphur-dioxide, dichloroethylene, dichlorodifluoromethane, methane, ethane, ethylene, propane and butane.

6. A method as claimed in claim 1 in which the second fluid is ammonia, and the third fluid is water.

References Cited in the file of this patent FOREIGN PATENTS 

1. A METHOD OF COOLING A FIRST FLUID WITH A SECOND FLUID WHICH COMPRISES: (A) PASSING THE SECOND FLUID AS A LIQUID AT A TEMPERATURE LOWER THAN THAT OF THE FIRST FLUID IN INDIRECT HEAT EXCHANGE WITH THE FIRST FLUID, THE PRESSURE OF THE SECOND FLUID BEING SUCH THAT IT REMAINS AS A LIQUID THROUGHOUT SUCH HEAT EXCHANGE STEP; (B) EXPANDING THE WARMED SECOND FLUID FROM THE HEAT EXCHANGE STEP IN A PLURALITY OF EXPANSION CHAMBERS IN SERIES TO PRODUCE A COLD SECOND FLUID AS A LIQUID AND, FROM EACH EXPANSION CHAMBER, A COLD SECOND FLUID AS A GAS; (C) RECOMPRESSING THE LIQUID FROM STEP (B) AND RECYCLING IT TO STEP (A); (D) RECOMPRESSING AND LIQUEFYING THE GASES FROM STEP (B), SAID LIQUEFACTION BEING EFFECTED BY INDIRECT HEAT EXCHANGE WITH A THIRD FLUID, AND (E) RECYCLING THE COMPRESSED LIQUID FROM STEP (D) TO THE EXPANSION CHAMBERS OF STEP (B). 